Actually when you look at ammaji as Sherni Sia cannot really be called one. She has a few more deeds to accomplish before she can be called sherni and same goes for Raghav to be called Sher. If Raghav would have saved Sia single handedly we could have called him Sher.
Regarding Sia winning Ammaji's dil, Ammaji is a very cruel person and such aperson is going on commiting henious crimes again and again despite opposition. So it is duty of every son, daughter, daughter in laws to stop ammaji from committing such henious crimes. Sia has tried all her best to get into ammaji's brain that she is commiting henious crimes and so have raghav sometimes but she just does not stop. So please tell me what other option does Sia-Raghav have then to oppose ammaji. They are highly qualified so could have easily found job in India or abroad but they did not run away from their responsibilities. Sia is just trying to stop attrocities of ammaji by becoming mukhiya of the village. She and Raghav still respect and love ammaji as a family member but as a citizen and a human being it is every humans right to fight atrocities committed on other humans whether they are their family or otherwise.
Regarding Sia understanding Raghav's dard of being away from his family, yes Raghav still loves his mother and other family members very much. But Raghav has also realized that as a dutiful son it is his duty to prevent his family from committing any more atrocitites and hiding them from law like in Gajinder case. If he stays back in house his mother and brothers will force him to commit crimes by blackmailing him like during Santosh episode. Raghav knows this very well and hence on supported Sia who was right. He did not say i am leaving this house and cutting all realtions with his family. Ammaji told him to get out of the house and he just obeyed her. Even if Rgahav was not married to Sia he would have been thrown out of the house one day bya ammaji for opposing her decisions. Santosh has seen raghav from childhood and they have more of an elder sister/mother-son kind of bond and have spent many years in that haveli. Hence she can understand his pain easily. Its not that Sia does not understand his pain but she has not yet revealed this to him. And remember Sia is young and still not that mature in relationships and life as Santosh is.
Ammaji has many times backstabbed and attacked her targets from the back.
Ex: She got Sunita killed in court by Raghav when she was in jail
She announced Sonali's engagement to Raghav without asking him
She sent Jhumar and many other ladies of village to DM to hide her crimes
She got Sheela chachi hit by 100 lashes for hiding Jhumar birth but what punishment she gave herself for keeping Amba alive
She nicely chased away amba without giving her rights because ammaji's satta was in trouble f amba stayed back
She forced Raghav to spend a night with Santosh by threatening to kill her if Raghav did not obey
She threatened Chanda to give false witness in court
Ammaji has always done things in sly though others understand finally it was her ideas later. I feel she only arranged Sia's kidnapping and acting goody in front of others. Even Shera is her guy who will cheat Sia finally i feel.
I think whoever as a mature individual stays in that house and not oppose ammaji is a equal bad human. I think the other good people must also leave haveli instead of having conference in bedrooms.
In this world a man is known by the deeds he does not by his family reputation. Like a bad person son can become good and a good person son can become bad. Valmiki was a daku who became a great and revered saint because of his deeds. Hence all must choose a good path to live irrespective of their family background. That is the message of this serial.